1. Field of the Invention
This invention relates to a method of locating a member in a borehole and is particularly, but not exclusively, concerned with boreholes which are substantially horizontal and have been drilled in seams such as coal seams. The invention is however able to be applied to boreholes at different dispositions without departing from the principles of the method.
2. Prior Art
In many mining applications it is a feature of the mining operation to determine the quality of a mineral such as coal in a seam well ahead of the extraction process. This is done to ensure the quality of the seam and to make sure that it is regular and that no faults or dirt inclusions are ahead of the mining operation. With an advance knowledge of the quality of the seam being mined, mine managers can plan their production in a most effective and efficient way to ensure the maximum extraction of useful wanted material. One method of assessing the quality of the seam currently in use, is to use an in-seam seismic system where a long borehole, typically up to a 1000 m in length, is drilled along one edge of a panel in the seam and a parallel borehole is drilled at the other edge of the panel. In the first borehole noise sources such as exploders are situated and in the second hole detectors such as geophones are positioned at known spaced distances. When the noise from the sources is transmitted through the area of the seam between the two boreholes the noise wave is attenuated according to the quality of the seam and any faults or foreign matter in the seam can cause a deflection on the wave received. The received wave is converted by the geophone into electrical signals which are transmitted over a cable to a remotely positioned recorder where the information is recorded and then analysed using computer techniques.
One of the problems which exists is to ensure that the detectors are spaced at the correct positions along the borehole and since these boreholes are very narrow, typically 3 inches in diameter, it is apparent that there is not much room for manoeuvring the detectors.
It is an object of the present invention to provide a method of locating a member in a borehole which enables the member or plurality of members to be spaced accurately within the borehole in both the correct location and orientation.